1. Field of the Invention
This invention relates generally to bus bar systems and, in one particular embodiment, to a bus bar system particularly suited for an aircraft transparency.
2. Technical Considerations
It is known to apply a conductive coating to a vehicle transparency, such as a vehicle windshield or window. When electrical current is supplied to the conductive coating, the coating temperature increases, which can provide deicing or defogging for the transparency. Electrical current is typically supplied to the conductive coating via one or more “bus bars” connected to a source of electricity. These bus bars can be metal or ceramic strips applied to a surface of the transparency and in contact with the conductive coating. In one known configuration, conductive ceramic bus bars are formed on a glass substrate, typically near the periphery of the substrate. The conductive coating is then applied over the surface of the substrate, including the bus bar. Electrical current supplied to the bus bar is transferred to the conductive coating to increase the coating temperature.
While this known system provides advantages over non-coated transparencies, there are still problems associated with this system. For example, the difference in thickness between the conductive coating and the bus bar may be as high as 1:200 to 1:400. Therefore, when the relatively thin conductive coating is formed over the much thicker bus bar, the coating formed at the transitional edges of the bus bar (i.e. the “film/bus bar junction”) can be thin, weak, or can contain discontinuities. These film/bus bar junction defects, in a worse case scenario, could lead to gaps or holes in the coating at the film/bus bar junction that can result in non-uniform transfer of electrical current and/or localized excessive current flow leading to resistance heating followed by arcing sufficient to damage the substrate.
Therefore, it would be advantageous to provide a bus bar system that eliminates or reduces at least some of the problems associated with conventional bus bar systems.